Experimental studies on the optimization of electric field distribution in an IH Lineac

The interdigital H type structure has been well known for its high shunt impedance at low β value. However, when a lineac system with a large beam energy gain is designed by adopting this structure, because of the development of particle velocity in the lineac, the ratio of the length of the first cell to that of the final cell becomes much larger than that of beam energy boosters. The electrostatic capacitance of drift tubes, and as the result, accelerating field strongly concentrate on the low energy region of the cavity. Focusing elements are indispensable for such high energy gain design. However, this fact makes drift tube diameter and the capacitance large, which affects the focusing power of quadrupole lenses. An optimum guideline was studied by the experiment using 1/4 scale models and by the theoretical calculation of particle orbits to design a device for flattening an accelerating field, drift tube quadrupole magnets and beam acceptance of the structure. The prototypes of the quadrupole magnets of tape coil type and plate spiral coil type were constructed and tested. Now, this lineac system is under construction, and will be completed in April, 1984. The specification and the structure of the lineac are shown. (Kako, I.)